Power vented water heaters are often equipped with intermittent burner ignition devices such as spark or hot surface igniters that ignite the pilot or main burner system only when there is a demand for hot water. Alternatively, the pilot burner may continuously operate in standing pilot type of ignition systems. Standing pilot ignition systems are less energy efficient and are manually re-lit after a power outage. This results in a significant preference in the market place for intermittent ignition systems.
However, intermittent ignition systems pose challenges regarding reducing the likelihood of igniting flammable vapors outside the power vented water heater since typical flame arrestor technology using intermittent ignition systems has proven challenging for a number of reasons. A power vented water heater typically uses a blower positioned directly above the flue to move combustion products from the ambient space surrounding the heater into the water heater and exhaust the products of combustion outside. Typical power vented water heaters have two sources of intake air. One source is for combustion, wherein combustion air flows through the combustion chamber and flue. One source causes air to flow directly into the blower to reduce the temperature of the exhaust gases. This allows the vent system to utilize PVC, ABS or CPVC venting. When the water heater burner is off, i.e., in standby mode, the blower does not operate nor is there pilot or main burner operation. When there is a call for heat, the blower typically operates for a short pre-purge period to establish that there is sufficient airflow through the water heater system to support combustion and vent combustion products outside. Measures have been taken to minimize the likelihood that flammable vapors, located in the vicinity of the water heater, could be drawn into the combustion chamber and ignited by the burner or igniter (reference U.S. Pat. No. 6,662,661, Fuel-Fired Heating . . . ). However, in the highly unlikely event that flammable vapors may be present at a location above the water heater, additional measures could theoretically be helpful.